Bio-inspired FeN5 moieties anchored on a three-dimensional graphene aerogel to improve oxygen reduction catalytic performance

Abstract

Transition-metal-coordinated nitrogen-doped carbon (M-N-C) materials have been regarded as the most promising oxygen reduction reaction (ORR) catalysts. However, the ambiguity of the exact active sites seriously hampered the understanding of the structure–performance correlation and the further activity improvement of M-N-C catalysts. Herein, we designed and synthesized a three-dimensional graphene aerogel (GA) supported FeN₅ composite with an explicit five-coordinated Fe–N bond. In this composite, pyridine groups were covalently grafted on the graphene surface to anchor iron phthalocyanine (FePc) molecules (FePc/AP-GA). The ORR performance of this catalyst showed a half-wave potential of −0.035 V (vs. Hg/HgO) in an alkaline electrolyte, which surpassed those of the benchmark Pt/C and most pyrolyzed or non-pyrolyzed nonprecious metal catalysts. Additionally, the FePc/AP-GA composite also exhibited a high kinetic current density of 20.01 mA cm⁻² at −0.1 V, good durability, and high tolerance to methanol poisoning effects. X-ray absorption spectroscopy results revealed that the five-coordinated Fe–N bond dominated in the FePc/AP-GA composite with an elongated bond length. This geometric and electronic structure of the iron atom in the FePc/AP-GA composite is believed to facilitate the adsorption of O₂ and intermediates and thus to enhance ORR activity and durability. Our results provided a promising target active site for the rational design of highly efficient M-N-C catalysts for fuel cells and metal–air batteries.